Abstract: Climate and vegetation changes profoundly affect the regional water cycle by altering precipitation patterns, evapotranspiration processes, and underlying surface conditions.Baseflow (Q_b), as a crucial component of runoff (Q), exhibits greater sensitivity to these changes than total runoff.However, previous studies have focused on responses of Q to changing environments; those of Q_b remain understudied and highly uncertain.Thus, this study systematically assesses the impacts of climate change and vegetation dynamics on Q and Q_b using eight different baseflow separation methods and eight impact assessment methods across 12 groups of paired catchments in Australia.Results showed that: ① In afforestation catchments, both Q and Q_b decreased; in deforestation catchments, both Q and Q_b increased; in catchments with vegetation conversion, Q and Q_b initially increased, followed by a decline; whereas vegetation regeneration catchments exhibited divergent trends due to multifactorial controls.② Notably, vegetation changes influenced baseflow more than total runoff, with mean contribution rates of 52.3%~96.9% (Q_b) versus 48.3%~93.7% (Q).The highest contribution value was observed in deforestation catchments, and the lowest in vegetation regeneration catchments.③ Methodological variability in baseflow separation and impact assessment markedly affected the contribution values, with greater divergence arising from impact assessment methods than from baseflow separation methods.The contribution differences among methods varied by catchment, ranging from 8.0% to 92.0%.